The present invention relates to a structure of a heat pipe type heat exchanger.
There is known a meandering capillary tube heat pipe different from an ordinary heat pipe. In the meandering capillary tube heat pipe, vapor bubbles and liquid droplets of working fluid are distributed alternately over the inside cavity of the capillary tube, filling and closing the inside of the capillary tube by the surface tension, and a pressure wave due to nucleate boiling at the heat absorbing portion generates vibrations of the vapor bubbles and liquid droplets along the longitudinal (or axial) direction so that heat is transferred from a high temperature side to a low temperature side. The heat transfer device of this type is disclosed more in detail in various forms in U.S. Pat. Nos. 4,921,041 and 5,219,020. The disclosures of these U.S. Patents are herein incorporated by reference. This type heat pipe shows excellent heat transporting performance even in a top heat mode in which the high temperature region is above the low temperature region. Furthermore, the capillary tube is flexible, and fins are not required. Accordingly, the meandering capillary type heat pipe can fulfill the recent demand for smaller size and lighter weight.
This meandering capillary tube heat pipe is used as a heat exchanger in a heat receiving portion or heat radiating portion in various heat exchanging equipment. As one example of related art, a Japanese Patent provisional Publication No. 7-30024 shows a large capacity "kenzan" type heat sink.
This heat sink is a kind of a heat exchanger in which a capillary heat pipe extends back and forth repeatedly between the heat absorbing high temperature region and the heat releasing low temperature region. FIG. 10 is a perspective view showing the structure of this heat sink. The heat sink shown in FIG. 10 has a heat receiving base plate 11 having a heat receiving surface 11-1 for absorbing heat from a heating member, cross bars 12 for transferring heat from the base plate 11, and a group of slender projections 13 each consisting of a l-shaped capillary tube segment serving as a heat pipe. This heat sink is similar in shape to a "kenzan" which is a spiked device (or frog) used to support stems in a flower arrangement. A heat releasing portion constituted by these projections 13 is cooled by a convection air flow 14. Each projection 13 has a projecting looped portion serving as a low temperature heat releasing side, and a base portion which is clamped by a pair of the cross bars 12 and which serves as a high temperature heat absorbing side.
In this heat sink, it is easy to further increase the capacity of the heat sink by increasing the height of the projections and increasing the number of turns (or the number of the projections). From the nature of the meandering capillary tube heat pipe, this heat sink can function properly without regard to the posture assumed in the mounted state. It is possible to mount this heat sink in such a posture that the projections 13 are placed horizontally or upside down. The direction of the convection flow of the cooling fluid may be right or left, or up or down. Irrespective of the direction of the convection flow, this heat sink can perform satisfactorily. The projections 13 further serve as cooling fins, so that there is no need for further providing fins. Therefore, this heat sink is small in size and light in weight for its heat releasing capacity.
In this heat sink, it is necessary to increase the number of turns in order to enhance the performance. This heat sink, however, requires a troublesome and time-consuming operation for arranging multitudes of the projection 13, and this requirement becomes more severe when the number of turns is to be increased to enhance the performance. Besides, this operation is unsuited for automatic process and impeditive to cost reduction. Furthermore, the forest of the pin-shaped projections 13 increases the pressure drop of the convection flow, and hence increases the load of a cooling fan. This heat sink is limited in improvement of the heat radiating capability because fins cannot be attached to the capillary tube. If the number of turns is increased too much, the pressure drop increases and the flow speed of the heat medium fluid decreases, resulting in a decrease in the heat radiating performance.